<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<style>
			div{
				width:800px;
				height:300px;
				background: red;
				/*opacity:0.3;*/
				                /*红  绿 蓝  透明度*/
				background: rgba(255,0,0,0.3);
			}
		</style>
	</head>
	<body>
		<div>123123</div>
	</body>
</html>
